1. Field of the Invention
The present invention relates generally to semiconductor integrated circuit manufacturing and, more particularly to a method of forming a dielectric film having at least Si—N, Si—C, or Si—B bonds on a semiconductor substrate by atomic layer deposition (ALD).
2. Description of the Related Art
SiC, SiCN, SiCO and other silicon carbide insulation films were adopted as etching stopper films and Cu diffusion blocking films for devices installed with Cu wirings. These films provided advantages in that their film characteristics could be changed by controlling the ratios of carbon, nitrogen and oxygen and that these films offered insulation resistance despite being thin and also allowed for control of dielectric constant at low levels. Those skilled in the art have been forming these silicon carbide films using plasma CVD, where the step covering property (coverage) with these films formed on semiconductor circuits having irregular surfaces has been approx. 70%. On the other hand, the aspect ratio, which represents the ratio of depth to opening width, has increased in line with the trend for finer wiring patterns and the coverage of film itself is expected to decrease further, and this expectation has given rise to the need to examine technologies to form films using atomic layer deposition (ALD) generally associated with better coverage. Behind this need is an increasing demand for formation of films on semiconductor circuits having irregular surfaces of high aspect ratios.
As insulation film forming technologies based on ALD, those for SiO and SiN have been common. While the SiO process involving oxidizing replacement is basically insensitive to effects of temperature, etc., and thus can be performed at relatively low temperatures to form film, the SiN process requires high temperatures for film to be formed because nitriding replacement does not occur easily due to the skeleton of the material used in this process, and as wiring patterns become finer, drop in replacement efficiency in the pattern and other undesirable outcomes lead to varying film qualities at different parts of the pattern as well as poor coverage.
In the ALD-based SiO process, in many cases aminosilane material is used as a precursor, while oxidizing gas is used as a reactant gas, to form SiO film of good quality. On the other hand, when the inventors of the present invention formed SiN film through the ALD-based SiN process using aminosilane material as a precursor and nitrogen gas such as N2 or NH3 as a reactant gas, and evaluated the formation of film, it was confirmed that the content of residual carbon in SiN film increased. In other words, despite its name of “SiN” the film contained a significant amount of carbon and other elements, and SiN film constituted virtually by Si, N and H was not formed. Since one likely reason for this residual carbon in SiN film is low nitriding efficiency, it is necessary to improve the process material before we can form SiN film containing less residual carbon.
As discussed above, the present inventors have recognized several problems in formation of a SiN film by ALD and developed solutions thereto, which solutions can also be applicable to formation of other types of film such as SiC, SiCN, SiBN, and SiBCN. Thus, the present invention relates to improvement on formation of films having Si—N, Si—C, and/or Si—B bonds.
Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and it should not be taken as an admission that any or all of the discussion were known at the time the invention was made.